1. Field of the Disclosure
The present disclosure relates to a touch panel and an image display device including the same, and more particularly, to a touch panel capable of reducing touch noise due to the phase differences of sensing signals output from touch ICs by adjusting the phase differences of the sensing signals, and an image display device including the touch panel.
2. Discussion of the Related Art
Recently, with the development of information society, demands in the display field are increasing in various forms. In order to meet the demands, studies into various slim, lightweight image display devices having low power consumption, for example, a liquid crystal display (LCD), a plasma display panel (PDP), and an electro luminescent display (ELD), have been conducted.
As a touch panel for the image display devices, an add-on type touch screen panel that is manufactured by attaching a touch panel on a display panel, or an on-cell or in-cell type touch screen panel that is manufactured by installing a touch panel in a display panel, is attracting attention.
Such a touch screen panel is used as an output device for displaying images while being used as an input device for receiving a user's command of touching a specific area of a displayed image.
For example, if a user touches a screen while viewing an image displayed by a display panel, a touch panel detects location information of an area at which the touch has occurred, compares the detected location information to the location information of the image, and transfers the detected location information to a system, etc. so as to recognize a user's command.
Touch panels are classified into various types according to different methods of detecting location information, including resistive type, capacitive type, infrared ray type, and ultrasonic type.
The capacitive type is classified into self capacitance type and mutual capacitance type.
A self capacitance type touch panel in which a plurality of sensing electrodes are formed on a base member detects the location information of an area at which a touch has occurred by sensing a change in capacitance in the sensing electrodes.
In the self capacitance type touch panel, the sensing electrodes are formed with a single layer structure, and each sensing electrode has unique coordinate information.
A mutual capacitance type touch panel in which a plurality of first and second sensing electrodes having different directivities are formed on a base member detects the location information of an area at which a touch has occurred by sensing a mutual change in capacitance in the first and second sensing electrodes that are dividedly arranged.
In the mutual capacitance type touch panel, the first and second sensing electrodes are formed with a multi-layer structure, and x-axis and y-axis coordinate information is detected from the individual first and second sensing electrodes.
In the case of the in-cell type touch screen panel which is installed in an image display device, the capacity of the internal capacitor is very large since the distance between sensing electrodes and gate lines or data lines is short.
Accordingly, the in-cell type touch screen has a problem in that if it senses location information according to the mutual capacitance type, it is greatly influenced by noise while having a small change in capacitance when a touch has occurred.
Hereinafter, an in-cell type touch screen panel which is a self capacitance type will be described with reference to FIG. 1.
FIG. 1 is a top view schematically showing a touch panel which is driven according to a self capacitance type according to the related art.
As shown in FIG. 1, the touch panel 1 may include a touch driver 10 and a touch unit 20.
The touch driver 10 outputs sensing signals to the touch unit 20 to sense a touch input.
The touch unit 20 may include a plurality of pattern electrodes 22 formed on an array substrate (not shown).
The pattern electrodes 22 operate as sensing electrodes for sensing a touch input during a touch period, and as common electrodes to which a common voltage is applied during a display period.
A plurality of output channels of the touch driver 10 may be connected to the respective pattern electrodes through connection lines 12.
For example, the touch driver 10 includes 40 output channels, and the individual output channels are connected to 40 pattern electrodes.
That is, as shown in FIG. 1, the pattern electrodes on the first through eighth rows may be connected to the first through eighth connection lines 12a through 12h. 
FIG. 2 is an equivalent circuit diagram of a touch unit included in a touch panel, and FIG. 3 is a view for explaining operation of sensing a touch according to the self capacitance type. The following description will be given with reference to FIGS. 1, 2, and 3.
Before a touch occurs (No Touch), gate capacitance Cgate and data capacitance Cdata are generated between the touch unit 20 of the touch panel and the gate lines GL, and between the touch unit 20 and the data lines DL, respectively, and also parasite capacitance Cothers is generated.
When a touch has occurred (Touch), as shown in FIG. 2, touch capacitance Cfinger is generated between the touch unit 20 and a touch input device (a user's finger or a touching unit).
Also, resistance R which is a sum of input resistance and panel resistance, is applied as a load to the touch unit 20.
Due to the change in capacitance of the touch panel, a time period taken for a sensing voltage Vo to be discharged to be a sensed voltage Vx before a touch occurs (No Touch) is different from a time period taken for a sensing voltage Vo to be discharged to be a sensed voltage Vx when a touch has occurred (Touch).
That is, as shown in FIG. 3, a time period taken for a sensing voltage Vo to be discharged to be a sensed voltage Vx before a touch occurs (No Touch) is “tx”, whereas a time period taken for a sensing voltage Vo to be discharged to be a sensed voltage Vx when a touch has occurred (Touch) is “tx+Δt” that is longer than “tx”.
The reason is because a sensing time period taken for a sensing voltage Vo to be discharged to be a sensed voltage Vx increases since the total capacitance of the touch unit 20 increases to “Cgate+Cdata+Cothers+Cfinger” when a touch has occurred.
Also, although shown in the drawings, due to the change in capacitance of the touch panel, a sensing time period taken for a sensing voltage Vo to be charged to be a sensed voltage Vx when a touch has occurred (Touch) also becomes longer than a sensing time period taken for a sensing voltage Vo to be charged to be a sensed voltage Vx before a touch occurs (No Touch).
As such, the self capacitance type touch panel determines whether a touch has occurred by comparing sensing time periods taken before a touch occurs and after a touch has occurred.
The in-cell type touch panel which is driven according to the self capacitance type requires a large number of pattern electrodes for increasing touch sensitivity.
However, existing touch drivers do not have a sufficient number of output channels that can be respectively connected to the increased number of pattern electrodes.